package bishi.day38_6_28;

import java.util.Scanner;

/**
 * @author 是阿秋啊
 * @date 2022/06/28 19:55
 **/
public class demo2 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            int m = sc.nextInt();
            int n = sc.nextInt();
            boolean[][] dp = new boolean[m][n];
            double[][] ret = new double[m][n];
            int k = sc.nextInt();
            for (int i = 0; i < k; i++) {
                int a = sc.nextInt() - 1;
                int b = sc.nextInt() - 1;
                if (!dp[a][b]) {
                    dp[a][b] = true;
                }
            }
            ret[0][0] = 1.0;
            for (int i = 0; i < m; i++) {
                for (int j = 0; j < n; j++) {
                    if (i == 0 && j == 0){
                    }else if (dp[i][j]){
                        ret[i][j]=0;
                    }else {
                        ret[i][j]=(j-1<0?0:(i+1<m?ret[i][j-1]*0.5:ret[i][j-1]))+(i-1<0?0:(j+1<n?ret[i-1][j]*0.5:ret[i-1][j]));
                    }
                }
            }
            System.out.printf("%.2f",ret[m- 1][n - 1]);
        }
    }
}